What common mistake do developers make with Cache invalidation, why does the mistake cause problems, and what is the safer approach?

What common mistake do developers make with Cache invalidation, why does the mistake cause problems, and what is the safer approach? One recurring problem with cache invalidation is applying it without understanding the boundary it protects. Caching mutable data forever and never defining when the cached value must be invalidated. In addition, Applications need a consistent strategy for removing or refreshing cache entries after source data changes. Safer engineering approach: keep the responsibility in the correct layer, use the framework's supported API, validate and authorize inputs, avoid hidden side effects, and verify the behavior with tests.